A macroscopic mechanical resonator operated in the quantum limit

The observation of quantum effects in a macroscopic mechanical resonator is hindered by the difficulty in cooling to the quantum ground state, and in making a system that displays adequate coherence times. We are able to meet these challenges in a novel system comprising a superconducting phase qubit coupled to a high frequency (6 GHz) micromechanical dilatational resonator. Using this coupled system, we place an upper bound on the minimum average phonon occupation number of the mechanical resonator $\langle n \rangle < 0.07$, showing that the resonator is in its quantum ground state. Furthermore, we use the qubit to both create and measure a single phonon state in the resonator. Using this ability, the energy decay and phase coherence times of the resonator are extracted. Additionally, we excite the resonator directly with a classical microwave source, demonstrably creating a coherent state in the mechanical resonator.